Watch a ‘sonic tractor beam’ do some midair sewing

Researchers have made a big leap in their quest to levitate objects using sound. Armed with two grids of loudspeakers, scientists have found a way to hold multiple objects in midair—and even do a bit of gravity-defying sewing.

Researchers have levitated single objects with sound before. Earlier this year, scientists built a “sonic tractor beam” that suspended a 16-millimeter-wide Styrofoam ball in the air.

Now, the same team has worked out how to hold, rotate, and move numerous objects in midair at the same time. Using two grids of 256 speakers and a novel computer algorithm they managed to independently manipulate up to 25 polystyrene balls 1 millimeter to 3 millimeters in diameter—about the size of small ants—at the same time, and use them to create such shapes as cubes and pyramids. To further demonstrate its precision, the scientists attached a piece of thread to two polystyrene balls and used the acoustic device to thread it through a hole in a piece of fabric, which was also floating in midair.

The technique, reported this week in the Proceedings of the National Academy of Sciences, has a variety of potential applications from delicate manipulation of samples in biological experiments to moving surgical tools, drugs, and kidney stones within the human body. Those medical applications could happen relatively soon, as the ultrasound produced by the speakers can safely penetrate biological tissue and is already used routinely in pregnancy scans.